1. Field of the Invention
The present invention concerns a method for washing an article to remove contaminations attached or adhered to the article. In other words, the present invention concerns a method for removing from the article, through washing, a wide variety of contaminations, in particular, oils and fats adhered to the article such as press molded products, typically oils and fluids used in molding and cutting processes; and foreign substances, typically cutting fragments. The present invention also concerns a downsized and energy-saving washing apparatus for carrying out the washing method of the present invention.
2. Description of the Related Art
In the production of electronics parts and mechanical parts, washing is generally applied to the parts as an article to be washed in order to remove contaminations adhered to the parts in order to ensure good qualities of the parts in the subsequent fabrication steps, and good qualities of the final products. A conventional method for washing the parts includes, for example, dipping the parts in a solvent capable of dissolving oils and fats such as a chlorinated solvent and a hydrocarbon solvent, or dipping the parts in an aqueous washing solution comprising an alkali or base, a surfactant and the like, or spraying such an aqueous washing solution to the parts.
Generally speaking, the washing system is classified into two groups, i.e., dry washing system and wet washing system. For example, a washing system using a washing solution is classified under the category “wet washing”. However, since it includes the washing step of the parts with a washing solution to remove the contaminations, the rinsing step to remove the used washing solution from the parts, the removing step of the used rinsing solution, and the drying step, the wet washing system has to be carried out with an increased number of the steps in comparison with the dry washing system, and thus is not a reasonable washing method. Further, since a much amount of energies are required in the wet washing system, there arise another problem of reducing an amount of exhausted carbon dioxide (CO2) gas, in other words, energy-saving problem.
Further, in addition to the dry washing system and wet washing system described above, the washing system may be classified in view of its washing mechanism. In such a case, the washing system is classified under the following two groups, i.e., washing relied upon a chemical function and washing relied upon a physical function. For the washing of parts, washing is frequently carried out based on a combination of the chemical function and the physical function in order to increase an efficiency of washing. That is, for the purpose of increasing an efficiency of washing, parts are dipped in a washing solution in order to chemically dissolve oils and fats in the solution, followed by applying a physical action such as ultrasonic treatment to the washed parts.
As an example, washing of heat exchanger products will be explained hereinafter.
For example, when the heat exchanger is made of aluminum-made parts, parts are produced from an aluminum material with press molding, and then the press molded parts are assembled to form an article having a desired shape, followed by subjecting the parts to a bonding step such as soldering in order to obtain a heat exchanger product. In such a production of the heat exchanger product, it is necessary to wash the press molded parts in order to remove from a surface of the parts a remainder of the fabrication oil used with the press molding and adhered to the parts, and cutting fragments (foreign substances), as well as fine or small particulates and/or burrs appearing on a cut surface of the parts. As is described in, for example, Japanese Patents No. 3030313 and 3030314, washing of the press molded parts as an article to be washed is carried out by immersing the parts in a washing solution, while continuously applying an ultrasonic radiation, in a continuous ultrasonic washing apparatus in order to peel off and remove the adhered contaminations from the parts. However, the washing methods described in these Japanese patent literatues suffer from drawbacks such as an increased level of energies consumed, a large-sized washing plant, and an increase of costs.
On the other hand, there is another washing method based on a compact peeling off/washing technology, according to which a super-cooled washing solution is sprayed against the parts. According to this washing method, the adhered contaminations can be peeled off and removed by spraying a super-cooled washing solution having a temperature of not more than its solidifying point from a spraying nozzle to the parts under an atmospheric pressure in order to peel off and remove the adhered contaminations from the parts. As is described in, for example, Japanese Patent No. 3323304, when it is contacted with the parts as an article to be washed, the washing solution in the state of a super-cooled washing solution can be changed from the super-cooled state to the corresponding solidified or frozen state. Upon freezing of the washing solution, a phase transfer of the washing solution from liquid to solid is caused with an expansion of the volume of the solution. As a result, the expanded and frozen washing solution can rub a surface of the parts in such a manner that the contaminations are removed from the surface of the parts.
Further, as is described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2008-264926, there is another washing method which comprises spraying to the parts a washing medium containing both the frozen particles of water and the liquid droplets in a super-cooled state from an ice blasting nozzle. The washing method is effective to remove small burrs from the surface of the parts.
However, when the super-cooled washing solution or medium containing both the frozen particles of water and the liquid droplets in a super-cooled state is sprayed against the parts of the heat exchanger product in order to wash the parts during washing process, there arises a problem that, after the washing process, liquid droplets formed upon melting of the frozen washing solution can remain on the washed parts. Further, a plurality of spraying nozzles have to be disposed at a multistage manner, thereby resulting in an increase of energies consumed, a large-sized washing plant, and an increase of costs. This is because press molding machine used in the production of the parts of the heat exchanger product can exhibit a highly increased production capability, and thus, when the press molding machine is directly disposed in combination with the subsequent washing plant, the washing plant has to be operated concurrently with the press molding machine, at the feeding speed of about 2 to 10 m/min. which is a speed of the longitudinal parts discharged from the press molding machine, while ensuring a high washing quality and a high washing speed.